Soft-start pump control system

ABSTRACT

A soft-start pump controller system for controlling a pump motor includes a switching device for supplying power to the pump motor; a periodic duty cycle generator for periodically actuating the switching device at a fraction of the full duty cycle to operate the pump at a reduced, quieter level; a sensor for sensing the current drawn by the pump motor; a reference circuit; and a liquid detector for detecting the presence of the liquid to be pumped, responsive to the sensor and the reference circuit, for overriding the periodic duty cycle generator and actuating the switching device to operate the pump motor continuously at full power when the motor current exceeds a predetermined level indicating liquid is present.

FIELD OF INVENTION

This invention relates to a soft-start pump control system for a pumpmotor which operates much more quietly and without the need for a floatswitch or other level sensing device.

BACKGROUND OF INVENTION

Bilge pumps, sump pumps and similar DC or AC electric powered pumps usedto pump out accumulated water traditionally use a float switch for thepump power circuit in which the water level raises and lowers the floatsufficiently to close and open the associated switch. Such float switchdevices require a number of moving parts which wear or bind andeventually fail; and the wearing and binding is often accelerated by thedamp, corrosive and dirty environment in which these float switches areused. Failure of the switch can have catastrophic effects since when thepump does not operate the water accumulates and can flood the area. Inthe case of bilge pumps, the flooding can sink the vessel.

One attempt to eliminate the need for such float switches includes meansto periodically, automatically, e.g. every five minutes, turn the pumpon whether or not there is water or liquid buildup. The pump current isthen monitored, and, if it is low, a no-load condition is detected andthe pump is shut off. If the current is normal, a load condition isdetected and the pump is permitted to keep pumping until the water isdrained and the low current condition reoccurs. See U.S. Pat. No.5,076,763, "Pump Control Responsive to Timer, Delay Circuit and MotorCurrent", by the present inventors. While this solves the float switchproblems, it adds another. Namely, in some installations the noise ofthe pump turning on every five minutes or for a similar time intervalannoys owners and crew. For, even if no water is present the pump stillrelentlessly makes noise every five minutes.

SUMMARY OF INVENTION

It is therefore an object of this invention to provide an improved pumpcontroller system.

It is a further object of this invention to provide such a pumpcontroller system which is simple and reliable, even in dirty,contaminated, hostile environments.

It is a further object of this invention to provide such a pumpcontroller system which operates periodically, automatically toeliminate the need for a float switch but which is quieter in operation.

It is a further object of this invention to provide such a pumpcontroller system combined with a pump to make a smaller, more compact,easy to install unit.

This invention results from the realization that a truly effective pumpmotor for periodically yet quietly operating a pump can be effected byautomatically energizing the pump motor at regular intervals but atreduced power by reducing the duty cycle while sensing the motor currentand then stepping up the power if the motor current amplitude indicatesthat there is liquid to be pumped. The invention can be effectivelyapplied to AC motor applications. In the same manner as DC motors, ACmotors also exhibit higher levels of current draw when pumping liquids.

This invention features a soft-start pump controller system forcontrolling a pump motor, which includes switching mean for supplyingpower to the pump motor and a periodic duty cycle generator forperiodically actuating the switching means at a fraction of the fullduty cycle to operate the pump at a reduced, quieter level. There aresensor means for sensing the current drawn by the pump motor, areference circuit, and a liquid detector for detecting the presence ofthe liquid to be pumped and responsive to the sensor means in thereference circuit for overriding the periodic duty cycle generator andactuating the switching mean to operate the pump motor continuously atfull power when the motor current exceeds a predetermined levelindicating liquid is present.

In a preferred embodiment the periodic duty cycle generator may includea duty cycle generator for providing a fractional duty cycle to theswitching means and a cycle timer for periodically operating the dutycycle generator. The duty cycle generator may provide a 30% duty cycle.The liquid detector may include a comparator responsive to the referencecircuit and to the sensor means. There may be an overload detectorresponsive to the sensor means and the reference circuit for overridingthe periodic duty cycle generator and the liquid detector to actuate theswitching means to deenergize the pump motor. The reference circuit mayinclude a reference adjustment means responsive to the liquid detectorfor adjusting the reference level as a function of the current drawn bythe pump motor under full power and at a fraction of the duty cycle.

DISCLOSURE OF PREFERRED EMBODIMENT

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a block diagram of a soft-start pump controller systemaccording to this invention; and

FIGS. 2A and 2B are a more detailed schematic diagram of the system ofFIG. 1.

There is shown in FIG. 1 a soft-start pump controller system 10 forcontrolling a pump motor 12 and switching circuit 14 which controls thepower to pump motor 12 supplied from power supply 15 which may consistsimply of battery 15a or may include a converter driven by an A.C.source. Current sensor 16 monitors the current flowing through pumpmotor 12 and provides an output on line 17. When the current flow islow, below a certain predetermined working or pumping level, then thepump motor is operating in a no-load condition and there is little or noliquid or water to be pumped. When the current sensor senses a currentflow at the working level, then the pump motor is under a load conditionand liquid, such as water, is present and therefore pumping is required.

Instead of a float switch which operates pump motor 12 only when thewater or other liquid has reached a predetermined level, system 10 usesa periodic duty cycle generator 18 which includes a cycle timer 20 and aduty cycle generator 22. Cycle timer 20 actuates duty cycle generatorperiodically, for example every five minutes. Actually any desiredperiod may be selected: less than one minute, one minute, two minutes;often a range of 1-3 minutes is satisfactory. At that time the dutycycle generator 22 delivers a signal on line 23 to operate switchingcircuit 14 to provide a fraction of the full power available to pumpmotor 12. This causes the pump motor to operate at a lower level and amuch quieter level. If during that periodic low-power operation liquiddetector 24 detects sufficient water or other liquid, necessitating theoperation of pump motor 12, a signal is provided on line 26 to overridethe signal on line 23 and cause switching circuit 14 to provide power topump motor 12 at the full available power. Liquid detector 24 respondsto the output from current sensor 16 to provide the override signal online 26 when the current reaches a predetermined level with respect tothe reference circuit 28, indicating that there is sufficient water orother liquid accumulated and ready to be pumped. The second detectorcircuit, overload detector 30, also responds to the current detected bycurrent sensor 16 and to reference circuit 28 to provide an output online 32 when the current exceeds a predetermined level indicating thatthe pump motor is in an overload mode, i.e., the pump is jammed or forsome other reason the pump motor is overloaded. The signal on line 32then overrides either signal on line 23 or 26 and turns off switchingcircuit 14 so that no more power is provided to pump motor 12 whichmight otherwise be damaged by the overload condition. RC timing circuit35 is included to extend the off signal on line 32 until the voltage online 17 falls below the water detection reference voltage of liquiddetector 24, preventing the circuit from oscillating. Timing circuit 35also prevents oscillations during the time when duty cycle generator 18is on and an otherwise periodic off signal would be on line 32.

Since the system can be operated at two power levels, the reduced powermode produced by duty cycle generator 22 and the full power modeproduced by the signal from low liquid detector 24, which overrides thesignal from duty cycle generator 22, some adjustment must be made toreference circuit 28. This is done by reference adjust circuit 34 whichoperates reference circuit 28 in the low power mode at all times exceptwhen liquid detector 24 determines that there is sufficient water orliquid present to operate pump motor 12 at full power. When this occurs,reference circuit 28 has its reference levels raised to coincide withthe increased power being supplied to pump motor 12 as explained morefully below.

A more detailed schematic of the embodiment shown in FIG. 1 appears inFIGS. 2A and 2B, where power supply 15 includes battery 15a and afiltering network 39 including diode 40 and filter capacitor 42. Theoutput V_(cc) of the filtering network 39 is the input to referencecircuit 28. Reference circuit 28 includes three resistors 42, 44 and 46,and a filter capacitor 48. Resistor 44 is the overload reference andresistor 46 is the liquid detector reference. Overload detector 30includes comparator 50 and diode 51 while liquid detector 24 includescomparator 52 and diode 53. Reference adjust circuit 34 includesamplifier inverter 54 and resistor 56, which connects directly toreference circuit 28. Cycle timer 20 includes amplifier inverter 60 witha feedback loop including resistor 62 and diode 64, and a discharge paththrough resistor 66 for capacitor 68. Diode 101 acts as a power offreset to allow capacitor 68 to discharge when the power is removed.Diode 70 interconnects cycle timer 20 and duty cycle generator 22. Dutycycle generator 22 also includes an amplifier inverter 72, with afeedback loop including resistor 97 and diode 98 and a discharge paththrough resistor 76 for capacitor 74. The output of amplifier 72 is fedto line 23 through resistor 78 to line 26, which is connected toswitching circuit 14. Switching circuit 14 includes three inverteramplifiers 80, 82 and 84, and a MOSFET power switch 86. Current sensor16 includes resistor 90 which provides a voltage at point 92 that is afunction of the current drawn through pump motor 12 and resistor 90.This voltage is delivered through a filter consisting of resistor 94 andcapacitor 96 to the input of both liquid detector comparator 52 and theoverload detector comparator 50.

Amplifier inverters U1A-U1F may be implemented with a Hex CMOS inverterchip, and the comparators U2A and U2B may be implemented with an LM358Noperational amplifier, both made by National Semiconductor. Diodes D1-D5may be 1N4148's, also made by National Semiconductor.

In operation, when the system is turned on, capacitor 68 is dischargedand inverter amplifier 60 has a high output since it has a low input.Amplifier 60 feeds back current through diode 64 and resistor 62 tocharge capacitor 68. During this time, while amplifier inverter 60 has ahigh output, diode 70 is back biased so that the input of inverteramplifier 72 in duty cycle generator 22 is low and its output is high.Thus amplifier 72 feeds back current through resistor 97 and diode 98 tocharge capacitor 74 and begins oscillating, in this example, at 120-150cycles per second. It will keep oscillating at this rate forapproximately one second while capacitor 68 comes to a full charge. Whenthat happens the high input to amplifier 60 causes a low output whichstops the charging cycle and begins the discharging cycle wherebycapacitor 68 discharges through resistor 66. This takes about fiveminutes. If during the time capacitor 68 is discharging power isremoved, capacitor 68 can then discharge through diode 101. This allowsthe periodic duty cycle generator 18 to begin oscillations immediatelyupon power being reapplied and not having to wait five minutes forcapacitor 68 to discharge through resistor 66. Thus every five minutes,for approximately one second, periodic duty cycle generator 18 providesa 120-150 cycle signal on line 23. Each time the 120-150 cycle signal online 23 goes high, the output of amplifier So goes low, the output ofamplifier 82 goes high, and the output of amplifier 84 goes low, thuskeeping open switch 86 and cutting off current to motor 12. During theother portion of each cycle the input to amplifier 80 is low so that itsoutput is high, the output of amplifier 82 is low, and the output ofamplifier 84 is high, thus closing switch 86 and energizing pump motor12. During this periodic one-second interval, pump 12 is operated atapproximately 30% of its full power because of the 30% duty cycle of its120-150 cycle signal provided by duty cycle generator 18 on line 23. Thepump motor is thus operated at one third power and provides a softer,quieter operation mode at start-up.

If during that one-second interval there is sufficient water present sothat pump motor 12 draws a substantial amount of current, this will bereflected in the level of voltage across resistor 90 at point 92. Thissignal delivered on line 17 to comparator 52 is compared to thereference level provided by resistance 46, and, if the current is abovea predetermined level indicating that there is sufficient water to bepumped, the output of comparator 52 goes low, causing diode 53 to beforward biased, thereby pulling down the input to amplifier 80 so thatits output goes high. Thus the output of amplifier 82 goes low and theoutput of amplifier 84 goes high, closing switch 86 and overriding thepresence and the absence of the 120-150 cycle signal on line 23: whilethe periodic duty cycle generator 18 continues to cycle one second on,five minutes off, the reset of the system does not respond to thisaction. It simply responds to the signal on line 26 and continues topump at full power, until the water has been removed. At that point, thecurrent drops and when the voltage at point 92 is low enough, comparator52 will switch states so that it will have a high output, nowback-biasing diode 53 and providing a high output which provides a highinput to amplifier 80, causing it to have a low output so that amplifier82 has a high output and amplifier 84 has a low output. Now switch 86will only be turned on by the 120-150 cycle signal on line 23 forroughly 30% of the duty cycle during the one-second interval every fiveminutes.

Comparator 50 also responds to the voltage at point 92 indicative of thecurrent flow through resistor 90 in pump 12. Comparator 50 responds whenthe voltage at point 92 is above that provided by reference circuit 28.When the output of comparator 50 then goes high, diode 51 is forwardbiased which charges RC timing circuit 35, which includes capacitor 99,resistor 100 and diode 102, and provides an off signal on line 32. RCtiming circuit 35 prevents oscillation when over current conditions aredetected. This signal on line 32 automatically provides a high input toamplifier 84, whose low output then simply turns off switch 86 andceases all current flow to motor 12. This is done so that in the eventthat the pump becomes jammed or the motor is overloaded in any way thesystem will entirely shut down and prevent any further damage to thepump or pump motor.

A reference adjust circuit 34 uses amplifier 54 to sense when comparator52 is representing that there is sufficient water to be pumped. In thisevent, anticipating that pump 12 will be operated at full power,amplifier 54 through resistor 56 connects resistor 56 in parallel withresistor 42, thereby increasing the current flow through the voltagedivider of reference circuit 28 and increasing the voltage at thereference points. In this way the reference circuit 28 is shiftedbetween a low level, when the system is operating at a 30% duty duringthe one-second interval every five minutes, and a high level, when thesystem is operating at full power at any time when comparator 52 andliquid detector 24 determine that substantial water is present and causepump 12 to be turned on at full power.

Since the voltage V_(cc) supplied to voltage divider 28 is provideddirectly from power supply 15, any fluctuations in the voltage suppliedto pump 12 will be tracked by the voltage supplied to the voltagedivider of reference circuit 28. Since the reference circuit 28 and thepump 12 are subject to the same fluctuations, there will be no errorsintroduced by the change in the power supply voltage. Further, thepresence of reference adjust circuit 34 ensures that the difference inthe two modes of operation, that is, full power invoked by comparator52, and partial power when the system is operating under the samplinginfluence of duty cycle generator 18, does not cause false indicationsfrom overload detector 30. If it were not for the action of a referenceadjust circuit 34, comparator 50 would respond to currents in the normalpumping range as if they were indicative of an overload condition andprovide a signal to erroneously cut off power to pump 12.

While the example in this specific embodiment relates to a d.c. pumpmotor, similar operation can be effected with a.c. pump motors.

Although specific features of this invention are shown in some drawingsand not others, this is for convenience only as some feature may becombined with any or all of the other features in accordance with theinvention.

Other embodiments will occur to those skilled in the art and are withinthe following claims:

What is claimed is:
 1. A soft-start pump control system for controllinga pump motor comprising:switching means for supplying power to a pumpmotor; a periodic duty cycle generator for periodically actuating saidswitching means at a fraction of the full duty cycle, to operate thepump motor at reduced power for quieter operation; sensor means forsensing the current drawn by the pump motor; a reference circuit; andliquid detector means for detecting the presence of liquid to be pumped,responsive to said sensor means, and said reference circuit, foroverriding said periodic duty cycle generator and actuating saidswitching means to operate said pump motor continuously at full powerwhen the motor current exceeds a predetermined level indicating liquidis present.
 2. The soft-start pump controller system of claim 1 in whichsaid periodic duty cycle generator includes a duty cycle generator forproviding a fractional duty cycle to said switching means and a cycletimer for periodically operating said duty cycle generator.
 3. Thesoft-start pump controller system of claim 2 in which said duty cyclegenerator provides a 30% duty cycle.
 4. The soft-start pump controllersystem of claim 1 in which said liquid detector includes a comparatorresponsive to said reference circuit and said sensor means.
 5. Thesoft-start pump controller system of claim 1 further including anoverload detector responsive to said sensor means and said referencecircuit for overriding said periodic duty cycle generator and saidliquid detector to actuate said switching means to deenergize the pumpmotor.
 6. The soft-start pump controller system of claim 1 in which saidreference circuit includes a reference adjustment means, responsive tosaid liquid detector, for adjusting the reference level as a function ofthe current drawn by the pump motor under full power and at a fractionof the duty cycle.
 7. A soft-start pump controller system forcontrolling a pump motor, comprising:a switching device for supplyingpower to the pump motor; a periodic duty cycle generator forperiodically actuating said switching device at a fraction of the fullduty cycle; a current sensor for sensing the current drawn by the pumpmotor; a reference circuit; and a liquid detector for detecting thepresence of liquid to be pumped by the pump motor, responsive to saidcurrent sensor, and said reference circuit.
 8. A soft-start pump controlsystem for controlling a pump motor comprising:switching means forsupplying power to a pump motor; a periodic duty cycle generator forperiodically actuating said switching means at a fraction of the fullduty cycle, to operate the pump motor at reduced power for quieteroperation; sensor means for sensing the current drawn by the pump motor;a reference circuit; liquid detector means for detecting the presence ofliquid to be pumped, responsive to said sensor means, and said referencecircuit, for overriding said periodic duty cycle generator and actuatingsaid switching means to operate said pump motor continuously at fullpower when the motor current exceeds a predetermined level indicatingliquid is present; and a reference adjustment means, responsive to saidliquid detector, for adjusting the reference level of the referencecircuit as a function of the current drawn by the pump motor under fullpower and at a fraction of the duty cycle.